1. Field of the Invention
The present invention relates to novel chiral ligands derived from 3,3′-substituted biaryl phosphines and phosphinites. More particularly, the present invention relates to transition metal complexes of these chiral phosphine ligands. The transition metal complexes are useful as catalysts in asymmetric reactions, such as, hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition, epoxidation, kinetic resolution and [m+n] cycloaddition.
2. Description of the Prior Art
Discovery of new chiral ligands is crucial in developing highly enantioselective transition metal-catalyzed reactions. Many chiral ligands have been made for applications in asymmetric catalysis, however, relatively few of these chiral ligands are commonly used in industry for the synthesis of chiral molecules.
Several chiral ligands having a biaryl backbone are known in the prior art. These are summarized below: 
Among these ligands, BINAP (1) is one of the most frequently used chiral ligands. The axially dissymmetric, fully aromatic BINAP has demonstrated to be highly effective for many asymmetric reactions (Noyori, R. et al. Acc. Chem. Res. 1990, 223, 345, Ohkuma, T. et al. J. Am. Chem. Soc. 1998, 120, 13529). Recent results show that partially hydrogenated BINAP with a larger bite angle, H8-BRNAP (2), is a better ligand for certain asymmetric reactions due to restriction of conformational flexibility (Zhang X. et al. Synlett 1994, 501). Chiral BINAPO (3) was made and it was not effective due to the conformational flexibility (Grubbs, R. et al. Tetrahedron Lett. 1977, 1879). Other axially dissymmetric ligands such as BIPHEMP (4) and MeO-BIPHEP (5) were developed and used for a number of asymmetric reactions (Schmid, R. et al. Pure & Appl. Chem. 1996, 68, 131; Schmide, R. et al. Helv. Chim. Acta, 1988, 71, 897). However, the present inventor is not aware of any examples of related 3,3′ substituted chiral biaryl phosphines, the subject of the present invention, being disclosed in the prior art (Broger, E. A. et al., WO 92/16536 and Broger, E. A. et al., WO93/15089). NAPHOS (6), another example of a prior art compound has been prepared (Tamao, K. et al. Tetrahedron Lett. 1977, 1389) and was found to be not effective for asymmetric hydrogenation reaction. The corresponding ligands with the N linker, BDPAB (7) and H8-BDPAB (8) have also been made and tested for asymmetric hydrogenation reactions (Zhang. F. et al. J. Am. Chem. Soc. 1998, 120, 5808).